Bleaching formulations comprising encapsulated organic peracids are known. For example, Nielsen et. al. disclose in U.S. Pat. No. 3,494,787 a dry composition of matter having a core of perphthalic acid and an encapsulating layer of a hydrated water-soluble salt. The encapsulating layer prevents contact of the core with materials (e.g., alkalis) which cause its decomposition.
Inert salt diluents have been suggested for inclusion in the encasing layer of granulated compositions having cores containing perphthalic acids or perphthalic acids with inert diluents, viz., peracids admixed with peracid decomposition products (see U.S. Pat. No. 3,494,786 issued to D. R. Nielsen). While the presence of inert salt diluents in the encasing layer is effective in increasing the solution rate of the encasing layer, their presence does not appreciably increase the rate of solution of the less soluble core. An undesirable feature of slow core dissolution is that localized high concentrations of bleaching agent during laundering may be produced due to entrapment of solid particles in folds of cloth which may result in localized overbleaching and production of white spots on colored goods.
Diperisophthalic acid (DPI) has been described as having two different crystal forms defined by characteristic X-ray diffraction powder pattern spacings (see U.S. Pat. No. 3,880,914 issued to D. R. Nielsen, which disclosure is incorporated herein by reference). Each crystal form of DPI has a symmetry of structure which is usually associated with an external symmetry or "habit." The habits of DPI have been identified and designated as "tabular" and "acicular." The tabular habit DPI is characterized by a shape having two approximately equal dimensions with the third dimension about one-fifth to one-third the other dimensions. This habit is in contrast to the acicular (needlelike) habit DPI crystal having a typical length to diameter ratio of over 20.
U.S. Pat. No. 3,655,738 issued to D. R. Nielsen teaches a method of preparing tabular form DPI. In addition, our copending application Ser. No. 633,184, filed Nov. 19, 1975, now U.S. Pat. No. 4,052,443, discloses that water slurries of tabular habit DPI are formed or maintained by heating DPI slurry above about a temperature of 67.degree. C.
A method of increasing the dissolution rate of organic peracid cores in encapsulated formulations is needed.